Cards are a common organizing unit for modern user interfaces (UI). At their core, they’re just rectangular containers with borders and padding. However, when utilized properly to group related information, they help users better digest, engage, and navigate through content. This is why most successful dashboard/UI frameworks make cards a core feature of their component library. This article provides an overview of the API that bslib provides to create Bootstrap cards.
Setup code
To demonstrate that bslib cards work outside of Shiny (i.e., in R Markdown, static HTML, etc), we’ll make repeated use of statically rendered htmlwidgets like plotly and leaflet. Here’s some code to create those widgets:
library(bslib)
library(shiny)
library(htmltools)
library(plotly)
library(leaflet)
plotly_widget <- plot_ly(x = diamonds$cut) %>%
config(displayModeBar = FALSE) %>%
layout(margin = list(t = 0, b = 0, l = 0, r = 0))
leaflet_widget <- leafletOptions(attributionControl = FALSE) %>%
leaflet(options = .) %>%
addTiles()Shiny usage
Cards work equally well in Shiny. In the examples below, replace plotly_widget with plotlyOutput() and leaflet_widget with leafletOutput() to adapt them for Shiny server-rendered plots/maps.
Hello card()
A card() is designed to handle any number of “known” card items (e.g., card_header(), card_body(), etc) as unnamed arguments (i.e., children). As we’ll see shortly, card() also has some useful named arguments (e.g., full_screen, height, etc).
At their core, card() and card items are just an HTML div() with a special Bootstrap class, so you can use Bootstrap’s utility classes to customize things like colors, text, borders, etc.
card(
card_header(
class = "bg-dark",
"A header"
),
card_body(
markdown("Some text with a [link](https://github.com)")
)
)Some text with a link
Implicit card_body()
If you find yourself using card_body() without changing any of its defaults, consider dropping it altogether since any direct children of card() that aren’t “known” card() items, are wrapped together into an implicit card_body() call.1 For example, the code to the right generates HTML that is identical to the previous example:
card(
card_header(
class = "bg-dark",
"A header"
),
markdown("Some text with a [link](https://github.com).")
)Some text with a link.
Restricting growth
By default, a card()’s size grows to accommodate the size of it’s contents. Thus, if a card_body() contains a large amount of text, tables, etc., you may want to specify a height or max_height. That said, when laying out multiple cards, it’s likely best not to specify height on the card(), and instead, let the layout determine the height layout_column_wrap().
Although scrolling is convenient for reducing the amount of space required to park lots of content, it can also be a nuisance to the user. To help reduce the need for scrolling, consider pairing scrolling with full_screen = TRUE (which adds an icon to expand the card’s size to the browser window). Notice how, when the card is expanded to full-screen, max_height/height won’t effect the full-screen size of the card.
card(
max_height = 250,
full_screen = TRUE,
card_header(
"A long, scrolling, description"
),
lorem::ipsum(paragraphs = 3, sentences = 5)
)Adipiscing commodo vestibulum vulputate fames per cursus nisl luctus tempor blandit? Hendrerit gravida potenti arcu commodo velit cras, orci, morbi sapien risus cum facilisi. Eros posuere torquent suscipit himenaeos per montes rhoncus, vehicula lacinia laoreet. Sodales natoque vel ridiculus ultricies montes leo magna dignissim eget per. Tempus tristique nostra, mauris proin vehicula ut cursus cras dictumst.
Adipiscing vehicula pulvinar morbi cubilia, enim quam posuere nibh: donec placerat ridiculus diam? Blandit tristique donec malesuada in natoque duis! Ac fermentum libero urna primis: integer nisl hendrerit tellus: eleifend vivamus pellentesque leo eget potenti. Litora metus nunc non quam sem, eros neque ante potenti auctor tristique magna ultrices. Suscipit orci.
Amet massa pellentesque rutrum. Platea fames lacus habitasse tempor, volutpat facilisis inceptos mattis tristique. Quisque ac quis erat aliquet sodales – erat maecenas erat augue sagittis fusce bibendum sagittis ligula. Elementum sollicitudin lacinia duis facilisis velit; at eu ridiculus mi. Congue parturient phasellus dictumst ante rhoncus, mollis dis, primis, sodales venenatis a mi non ultricies.
Filling outputs
A card()’s default behavior is optimized for facilitating filling layouts. More specifically, if a fill item (e.g., plotly_widget), appears as a direct child of a card_body(), it resizes to fit the card()s specified height. This means, by specifying height = 250 we’ve effectively shrunk the plot’s height from its default of 400 down to about 200 pixels. And, when expanded to full_screen, the plot grows to match the card()’s new size.
card(
height = 250,
full_screen = TRUE,
card_header("A filling plot"),
card_body(plotly_widget)
)Most htmlwidgets (e.g., plotly, leaflet, etc) and some other Shiny output bindings (e.g, plotOutput(), imageOutput(), etc) are fill items by default, so this behavior “just works” in those scenarios. And, in some of these situations, it’s helpful to remove card_body()’s padding, which can be done via spacing & alignment utility classes.
card(
height = 275,
full_screen = TRUE,
card_header("A filling map"),
card_body(
class = "p-0",
leaflet_widget
),
card_footer(
class = "fs-6",
"Copyright 2023 RStudio, PBC"
)
)Fill item(s) aren’t limited in how much they grow and shrink, which can be problematic when a card becomes very small. To work around this, consider adding a min_height on the card_body() container. For example, try using the handle on the lower-right portion of this card example to make the card taller/smaller.
This interactive example is a bit contrived in that we’re using CSS resize to demonstrate how to make plots that don’t shrink beyond a certain point, but this concept becomes quite useful when implementing page-level filling layouts (i.e., page_fillable()) with multiple cards.
card(
height = 300,
style = "resize:vertical;",
card_header("Plots that grow but don't shrink"),
card_body(
min_height = 250,
plotly_widget,
plotly_widget
)
)Troubleshooting fill
As you’ll learn more about in filling layouts, a fill item loses its ability to fill when wrapped in additional UI element that isn’t a fillable container. To fix the situation, use as_fill_carrier() to allow the additional element to carry the potential to fill from the card_body() down to the fill item.
Multiple card_body()
A card() can have multiple card_body()s, which is especially useful for:
- Combining both resizable and non-resizable contents (i.e., fill items and non-fill).
- Allowing each
card_body()to have their own styling (via inline styles and/or utility classes) and resizing limits (e.g.,min_height).
For example, when pairing filling output with scrolling content, you may want min_height on the filling output since the scrolling content will force it to shrink:
card(
height = 375,
full_screen = TRUE,
card_header(
"Filling plot, scrolling description"
),
card_body(
min_height = 200,
plotly_widget
),
card_body(
class = "lead container",
lorem::ipsum(paragraphs = 10, sentences = 5)
)
)Elit leo fames, erat justo nisl dapibus parturient feugiat. Dictum lacinia rhoncus non aenean convallis mi velit bibendum: a a torquent! Aliquet lacinia aliquet maecenas, nisl condimentum tortor malesuada ornare. Porta cras magna leo libero a proin: enim tristique montes! Auctor lobortis ad netus; sodales mi natoque at rutrum aenean egestas a.
Sit class potenti purus ac montes; phasellus, risus ligula ullamcorper torquent? Nulla sapien sollicitudin vivamus tristique fusce, varius – ridiculus aliquam augue ac. Nullam lobortis sagittis magna congue praesent interdum dis volutpat quam lectus id. Tincidunt primis natoque odio nam quisque cursus dictum luctus? Congue sagittis eget bibendum massa.
Ipsum turpis quam natoque diam phasellus enim a placerat. Integer convallis – gravida, fusce sodales imperdiet fusce! Feugiat consequat sagittis vulputate sapien magnis posuere imperdiet. Curae inceptos ornare: placerat et nisl ornare fringilla justo. Nulla aptent urna erat justo taciti vulputate torquent fusce vel cursus, duis nunc tellus, facilisis et proin sapien facilisi quam malesuada!
Amet ante fusce orci proin: turpis ullamcorper nullam consequat cum? Luctus proin conubia nunc arcu justo curae, litora nunc penatibus felis facilisi metus ornare. Suscipit vitae praesent habitasse donec, diam ligula mattis neque sociis consequat mattis! Penatibus risus erat nascetur class fames ligula gravida scelerisque lacinia primis! Magnis mus auctor magna.
Dolor proin sagittis ridiculus, vulputate euismod, metus dictumst imperdiet parturient. Nibh ridiculus primis lobortis lectus tristique tincidunt hendrerit fusce laoreet. Nec lacinia erat dictum eu ad suscipit – gravida mi pharetra. Dapibus vitae volutpat tempus pellentesque dignissim: vitae imperdiet feugiat vitae. Accumsan auctor consequat semper enim convallis urna tincidunt suspendisse.
Sit ultrices primis nisi est; odio condimentum, dignissim commodo suscipit quisque hac curae? Aenean hendrerit velit rhoncus, purus lacus – suscipit gravida sapien id quisque lacinia vehicula habitasse? Aliquet vel porttitor bibendum rutrum taciti donec per, viverra; neque dignissim dictum. Dignissim in velit lacus est auctor lobortis euismod fringilla molestie nostra? Auctor lobortis enim.
Dolor praesent donec dui eros auctor, enim dignissim eleifend cubilia taciti? Ac parturient eleifend rutrum erat libero mattis erat aptent id. Himenaeos nascetur at semper curabitur, nascetur aliquam dictum taciti rhoncus ultricies? Commodo ornare interdum tellus sed sapien vestibulum scelerisque faucibus. Dui metus facilisis proin magnis ut suspendisse quis – sapien, mi arcu sed morbi faucibus rhoncus massa mi condimentum cras porta.
Lorem habitasse id, nibh, suscipit diam scelerisque natoque porttitor! Tortor nulla massa hac cubilia conubia enim; ultrices conubia diam gravida odio, parturient nisl. Nibh lobortis magnis condimentum himenaeos facilisi vitae ornare nullam? Potenti porttitor sollicitudin ultricies: vestibulum semper vel mauris sagittis donec. Nam venenatis sagittis malesuada morbi tristique cras fringilla; nostra ut blandit, velit cubilia cum iaculis faucibus hendrerit luctus primis.
Consectetur duis ut etiam fusce ornare, libero urna. Sollicitudin auctor eget pretium ligula eros quisque. Velit bibendum pharetra eget – eu: velit imperdiet suscipit praesent nascetur! Sollicitudin rutrum magnis integer lacinia imperdiet justo nisl, sagittis scelerisque auctor? Justo blandit scelerisque, dis erat nisi nunc diam euismod curae natoque non dignissim, pharetra enim vivamus!
Consectetur etiam ad: duis ante torquent, nibh accumsan fringilla consequat taciti. Porttitor potenti mattis et; quis proin erat vulputate, nisi sociosqu accumsan aptent aliquet. Mattis pulvinar torquent, imperdiet mus lacinia feugiat quisque ut. Ac suscipit malesuada duis habitasse dictumst suspendisse sapien, arcu vel luctus? Sodales sed curae augue netus potenti convallis.
Also, when the content has a fixed size, and should not be allowed to scroll, set fill = FALSE:
card(
height = 350,
full_screen = TRUE,
card_header(
"Filling plot, short description"
),
plotly_widget,
card_body(
fill = FALSE,
card_title("A subtitle"),
p(class = "text-muted", "And a caption")
)
)A subtitle
And a caption
Multiple columns
As you’ll learn in column-based layouts, layout_column_wrap() is great for multi-column layouts that are responsive and accommodate for filling output. Here we have an equal-width 2-column layout using width = 1/2, but it’s also possible to have varying column widths.
card(
height = 350,
full_screen = TRUE,
card_header("A multi-column filling layout"),
card_body(
min_height = 200,
layout_column_wrap(
width = 1/2,
plotOutput("p1"),
plotOutput("p2")
)
),
lorem::ipsum(paragraphs = 3, sentences = 5)
)Consectetur arcu mauris platea sapien eget quisque dictumst venenatis tincidunt! Magnis ante ullamcorper viverra quis cubilia condimentum praesent litora. Erat ultricies semper class, primis quisque porta taciti. Purus praesent taciti convallis primis sodales commodo placerat commodo montes. Vestibulum velit nulla luctus ante vestibulum, aptent a maecenas.
Lorem sapien lacinia viverra: ultricies sollicitudin, fermentum lobortis euismod, felis ultricies per lacinia. Consequat eleifend viverra, justo est aenean netus libero bibendum id aptent. Fringilla aliquet aptent turpis nulla mollis vel aenean sagittis purus. Felis dui, molestie consequat tincidunt lobortis placerat imperdiet pharetra himenaeos! Maecenas ullamcorper quisque velit.
Lorem posuere, semper commodo facilisi turpis quisque, tempus magnis class. Ullamcorper mollis pretium eleifend orci facilisi arcu ligula sociis imperdiet. Magnis blandit nunc curae sociis sociis tincidunt. Metus cras inceptos ad auctor posuere turpis nunc enim. Mattis mauris nec semper ante tempor bibendum rutrum sed facilisis malesuada: risus class pulvinar quam!
Multiple cards
layout_column_wrap() is especially nice for laying out multiple cards since each card in a particular row will have the same height (by default). Learn more in column-based layouts.
layout_column_wrap(
width = 1/2,
height = 300,
card(full_screen = TRUE, card_header("A filling plot"), plotly_widget),
card(full_screen = TRUE, card_header("A filling map"), card_body(class = "p-0", leaflet_widget))
)Multiple tabs
navs_tab_card() and navs_pill_card() make it possible to create cards with multiple tabs or pills. These functions have the same full_screen capabilities as normal card()s as well some other options like title (since there is no natural place for a card_header() to be used). Note that, each nav() object is similar to a card(). That is, if the direct children aren’t already card items (e.g., card_title()), they get implicitly wrapped in a card_body().
library(leaflet)
navs_tab_card(
height = 450,
full_screen = TRUE,
title = "HTML Widgets",
nav(
"Plotly",
card_title("A plotly plot"),
plotly_widget
),
nav(
"Leaflet",
card_title("A leaflet plot"),
leaflet_widget
),
nav(
shiny::icon("circle-info"),
markdown("Learn more about [htmlwidgets](http://www.htmlwidgets.org/)")
)
)Sidebars
As you’ll learn more about in sidebar layouts, layout_sidebar() just works when placed inside in a card(). In this case, if you want fill items (e.g., plotly_widget) to still fill the card like we’ve seen before, you’ll need to set fillable = TRUE in layout_sidebar().
card(
height = 300,
full_screen = TRUE,
card_header("A sidebar layout inside a card"),
layout_sidebar(
fillable = TRUE,
sidebar(
actionButton("btn", "A button")
),
plotly_widget
)
)Static images
card_image() makes it easy to embed static (i.e., pre-generated) images into a card. Provide a URL to href to make it clickable. In the case of multiple card_image()s, consider laying them out in multiple cards with layout_column_wrap() to produce a grid of clickable thumbnails.
card(
height = 300,
full_screen = TRUE,
card_image(
file = "shiny-hex.svg",
href = "https://github.com/rstudio/shiny"
),
card_body(
fill = FALSE,
card_title("Shiny for R"),
p(
class = "fw-light text-muted",
"Brought to you by RStudio."
)
)
)
Shiny for R
Brought to you by RStudio.
Flexbox
Both card() and card_body() default to fillable = TRUE (that is, they are CSS flexbox containers), which works wonders for facilitating filling outputs, but it also leads to surprising behavior with inline tags (e.g., actionButton(), span(), strings, etc). Specifically, each inline tag is placed on a new line, but in a “normal” layout flow (fillable = FALSE), inline tags render inline.
card(
card_body(
fillable = TRUE,
"Here's some", tags$i("inline"), "text",
actionButton("btn1", "A button")
),
card_body(
fillable = FALSE,
"Here's some", tags$i("inline"), "text",
actionButton("btn2", "A button")
)
)That said, sometimes working in a flexbox layout is quite useful, even when working with inline tags. Here we leverage flexbox’s gap property to control the spacing between a plot, a (full-width) button, and paragraph. Note that, by using markdown() for the paragraph, it wraps the results in a <p> tag, which means the contents of the paragraph are not longer subject to flexbox layout. If we wanted, we could do something similar to render the actionButton() inline by wrapping it in a div().
card(
height = 325, full_screen = TRUE,
card_header("A plot with an action links"),
card_body(
class = "gap-2 container",
plotly_widget,
actionButton(
"go_btn", "Action button",
class = "btn-primary rounded-0"
),
markdown("Here's a _simple_ [hyperlink](https://www.google.com/).")
)
)Here's a simple hyperlink.
In addition to gap, flexbox has really nice ways of handling otherwise difficult spacing and alignment issues. And, thanks to Bootstrap’s flex utility classes, we can easily opt-in and customize defaults.
card(
height = 300, full_screen = TRUE,
card_header(
class = "d-flex justify-content-between",
"Centered plot",
checkboxInput("check", " Check me", TRUE)
),
card_body(
class = "align-items-center",
plotOutput("id", width = "75%")
)
)Shiny
Since this article is statically rendered, the examples here use statically rendered content/widgets, but the same card() functionality works for dynamically rendered content via Shiny (e.g., plotOutput(), plotlyOutput(), etc).
An additional benefit that comes with using shiny is the ability to use getCurrentOutputInfo() to render new/different content when the output container becomes large enough, which is particularly useful with card(full_screen = T, ...). For example, you may want additional captions/labels when a plot is large, additional controls on a table, etc (see the value boxes article for a clever use of this).
# UI logic
ui <- page_fluid(
card(
max_height = 200,
full_screen = TRUE,
card_header("A dynamically rendered plot"),
plotOutput("plot_id")
)
)
# Server logic
server <- function(input, output, session) {
output$plot_id <- renderPlot({
info <- getCurrentOutputInfo()
if (info$height() > 600) {
# code for "large" plot
} else {
# code for "small" plot
}
})
}
shinyApp(ui, server)Appendix
The following CSS is used to give plotOutput() a background color; it’s necessary here because this documentation page is not actually hooked up to a Shiny app, so we can’t show a real plot.